Torsen is permanently four wheel drive. Haldex is mainly front wheel drive until it starts to loose traction and then drive gets sent to the rear wheels also.
Torsen is generally seen as proper four wheel drive, but Haldex still does a good job because when needed the rear wheels spring into action very quickly.

iirc, Torsen is "all wheel drive" and Haldex is "four wheel drive". That doesn't really clear it up but basically a transfer box send some power to the front and some to the back in AWD, where as the 4WD system sends it all to the front until they spin at which point it lets some go to the rear. It's the difference between passive and permenant four wheel drive.

Think of it as Haldex is fwd with the back-up of rears when needed, but Torsen is 4wd and the power shifts depending on grip (and a couple of other things, like steering angle etc).

Wiki is your friend....Torsen - Wikipedia, the free encyclopediaHaldex Traction - Wikipedia, the free encyclopedia
The thing is that one is a proper diff(the Torsen or other torque sensing diffs such as the Quaife),and will allow much wider torque splits than the Haldex,and the Haldex has often been called a "part-time" 4WD system,which only allows a maximum 50/50 split.
The Torsen diff couldn't apprently be squeezed into the transverse mounted engine/gearbox of the A3 series,hence the Haldex electrohydraulic clutch is used instead.

The Haldex has been used in rallycross applications previously,with adjustable mapping,but it is limited in terms of torque split,whereas a torque sensing mechanical diff can have different torque splits such as 75/25 or whatever according to the biassing ratio.
Some torque biassing diffs can feel a bit "snappy" in use,and can give you a bit of a shock when you use one first,but the ability to direct torque to whichever wheel has grip is quite something.

Torsen is better but only found on A4/5/6/7/8, Q/5/7, R8 and maybe Q3?

From my knowledge, Haldex is actually a clutch which engages the rear wheels when the front looses grip where as the torsen is permanent 4wd.

Someone with better (and probably right!) knowledge of the systems will be along shortly

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Torsen is not "better" than haldex.. At least not the last two generations of it anyway.. They are different systems with drawbacks to both.. If haldex was no good it wouldn't be on cars like the Veyron and Lamborghini aventador.. The new version does not wait for wheels to slip- it is preemptive.

Torsen is not "better" than haldex.. At least not the last two generations of it anyway.. They are different systems with drawbacks to both.. If haldex was no good it wouldn't be on cars like the Veyron and Lamborghini aventador.. The new version does not wait for wheels to slip- it is preemptive.

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Nicely put....both have their good and bad points,and neither is perfect,but if you want more than a maximum 50/50 split,you need something other than the Haldex,whereas the Haldex can in some cases be more user-friendly,and need not be permanently engaged.

So for normal road driving the Haldex would appear to be a good enough system.
Cheers for the quick replies guys, as you can tell this is my first A3 Quattro, but it seems more refined than my previous Subaru Impreza's drivetrains.

you dont see any 4wd/4x4 related threads in the a4/6 sections saying its lost drive to the rear or locked up and dragging a back wheel round corners.

torsen just works.

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They both work,in different ways.

The stock Haldex though is way too slow,and biassed towards FWD,so what you need is the race controller,which removes all of that,and allows you to use it in stock,sport,and race modes,with the latter remaining engaged under braking as well,and also preloads the diff much quicker.

Totally different feel from the stock mode.

Oh,and mechanical diffs can wear out......all of them require maintenance,and if you try,breaking a diff,electronic or mechanical,it doesn't matter.
The Haldex on mine has dealt very well with 440-500+bhp,so i would say it's as robust as any mechanical diff I've used.

The stock Haldex though is way too slow,and biassed towards FWD,so what you need is the race controller,which removes all of that,and allows you to use it in stock,sport,and race modes,with the latter remaining engaged under braking as well,and also preloads the diff much quicker.

Totally different feel from the stock mode.

Oh,and mechanical diffs can wear out......all of them require maintenance,and if you try,breaking a diff,electronic or mechanical,it doesn't matter.
The Haldex on mine has dealt very well with 440-500+bhp,so i would say it's as robust as any mechanical diff I've used.

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Bit of a thread hijack but Alex is your S3 one of the quickest in the uk? Sounds awesome...

<tuffty/>Badger 5 Edition...Its all about the flow...Staff MemberModeratorAudi S3

Haldex cars don't eat rear tyres like torsion tends too... the gen 1 haldex on my 8L S3 is a bit agricultural but as Alex has said you can get uprated controllers... best of both worlds then...

Haldex needs proper maintenance though which is getting neglected quite a bit it seems on the 8L's at least these days... dunno what the intervals are on the 8P's but if not kept up the plates will stick..

The stock Haldex though is way too slow,and biassed towards FWD,so what you need is the race controller,which removes all of that,and allows you to use it in stock,sport,and race modes,with the latter remaining engaged under braking as well,and also preloads the diff much quicker.

Totally different feel from the stock mode.

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Performance controller (mated with the correct suspension/arb etc) is one of the best mods I EVER bought. At the end of the day, the system is setup as stock to be safe primarily. As mentioned in many previous discussions FWD has much more predictable driving characteristic (understeer!) for the novice driver in a loss of traction situation..:thumbsup:

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